Heidegger's nexus in the discussion of the idea of being in modern ontology is again Kant because Kant is halfway between the start (Descartes) and the latter's fulfilment (Hegel) and represents the keystone of its development following rationalism and idealism. Now, taking that thesis as the fundamental determination within the horizon from which modern ontology understands the problem of being and that of subjectivity, Heidegger examines how Kant understands and determines the structure of the subject.

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